Our tests are showing your router in sync at 80mbps. An SNR of 3db means that your line is pushing as much speed as it can to your router which is likely the reason why your router is in sync at the highest speed possible for FTTC.
Can you run a BT speedtest at http://www.speedtest.btwholesale.com using a wired connection, completing the further diagnostics at the end? This will store the result on the supplier system and will help us in reporting a fault to our suppliers.
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